Religion - the world would be a better place without it. It's caused more wars since the beginning of civilisation and many innocent people have been killed in its name (women burned as witches and children blown up in the name of jihad are classic examples of religious atrocities).
If it wasn't for religion we would still be tribal savages. I think the last two world wars has put to death (pardon pun) that myth. The vast majority of savagery thought time has been purely for territory gain.
p.s I'm an Atheist.